1. Field of the Invention
This invention relates to a magnet-type power generator mounted to an engine for motorcycles, all-terrain vehicles, snowmobiles, and outboard engines, and to a method of manufacturing the same.
2. Description of the Related Art
Recently, the engines to which a magnet-type power generator is mounted are required to have a longer lifetime for the purpose of quality improvement in the market. In particular, the rotor of the magnet-type power generator, fitted to the crankshaft, rotates at all times with the crankshaft. Therefore, if the rotor breaks, the function of the engine degrades and moreover the broken parts scatter, posing a danger to the driver. For this reason, the rotor needs particular attention so that it does not break even when used for a long time. The rotor of the magnet-type power generator has a magnet for generating magnetic flux and a flywheel, made of an iron-based material, for accommodating the magnet. Since the magnet easily fracture, a ring-shaped part of an iron-based material is generally added for the purpose of protecting and securing the magnet. However, only the ring-shaped part cannot secure the magnet completely, and the magnet may fracture when it is under the vibrations of the engine. For this reason, it is common to secure the magnet using an adhesive agent in combination with the ring-shaped part.
When securing the magnet with an adhesive agent, it is impossible to ensure stable bonding strength unless the adhesive agent is applied uniformly. Moreover, in order to harden the adhesive agent, a heating apparatus is necessary in the case of heat setting, or a long setting time is necessary in the case of cold setting. As a remedy for the problem, for example, in Patent Document 1, no adhesive agent is used, and the flywheel, the magnet, and the ring-shaped part are integrally molded with each other from a thermoplastic resin. In addition, in order to make the fabrication of the ring-shaped part easier and less costly and facilitate the assembling work, the ring-shaped part is made by bending a plate material. The technique of provisionally securing the position of the magnet by the ring-shaped part made by bending a plate material and thereafter integrally molding the flywheel, the magnet, and the ring-shaped part not only makes the assembling work easier but also can secure the magnet to completely at the same condition.
Patent Document 1: JP-UM-62-119179
Although the technique disclosed in Patent Document 1 can secure the magnet reliably and therefore makes it possible to increase the reliability, it requires an expensive non-magnetic material, such as SUS, to be used for the ring-shaped part, in order to prevent degradation of the magnetic characteristics. Moreover, in order to form a shape for provisionally securing the magnet to the ring-shaped part made by bending a plate material, a mold for progressive pressing is required when the productivity is taken into consideration. Furthermore, in order to mold a thermoplastic resin, a mold for injection molding is necessary. Another problem is that since the thermoplastic resin fills the gap between the flywheel and the ring-shaped part not just the surrounding portions of the magnet, the weight increases.